Rheostats

ABSTRACT

An encapsulated rheostat, particularly for data transmitters of filling level indicators in motor vehicle fuel tanks, has its resistive element enveloped in a resilient sheet of plastics material. A conductive inner layer is carried by the plastics sheet, and an adjustable contact pin presses against the sheet to establish localised contact between the conductive inner layer and the resistive element. The value of the electrical resistance of the rheostat is thereby variable by adjustment of the position of the contact pin. Air or other gas, or a liquid, confined within the encapsulating resilient plastics sheet tends to separate the resistive element and the conductive inner layer except at the region of localised contact provided by the adjustable contact pin. The resistive element may be of wire-wound construction, or may be resistive inner layer, possibly of strip form, carried by the plastics sheet.

United States Patent [191 Lehnert [451 Oct. 9, 1973 RHEOSTATS [75]Inventor: Gunter Lehnert, Russelsheim, Main,

Germany [7 3] Assignee: General Motors Corporation,

Detroit, Mich.

22 Filed: Sept. 18,1972

21 Appl. No.: 290,266

[52] U.S. Cl. 338/154, 338/199 [51] Int. Cl. H01c 5/00 [58] Field ofSearch 338/69, 154, 199

[56] References Cited UNITED STATES PATENTS 3,624,584 ll/l97l Ohno338/154 X 3,699,492 10/1972 Yoshihara 338/69 Primary Examiner-Bernard A.Gilheany Assistant Examiner-4). A. Tone Attorney-dean L. Carpenter eta1.

[5 7] ABSTRACT uid, confined within the encapsulating resilient plasticssheet tends to separate the resistive element and the conductive innerlayer except at the region of localised contact provided by theadjustable contact pin.

The resistive element may be of wire-wound construction, or may beresistive inner layer, possibly of strip form, carried by the plasticssheet.

7 Claims, 7 Drawing Figures RI-IEOSTATS This invention relates generallyto rheostats, and is particularly concerned with rheostat constructionsusable as data transmitters for filling-level indicators of fuel tanksin motor vehicles and aircraft.

Rheostats are used for a great diversity of purposes, such that there isfrequently a need to encapsulate the resistances thereof in order toprotect them from the effects of surrounding vapours or liquids, forexample. In particular, data transmitters which are fitted into fueltanks are exposed to such external influences, since they come directlyinto contact with the fuel or fuel vapours.

Objects of the present invention are to provide a rheostat constructionwhich gives protection from harmful external influences, is simple andinexpensive to produce, operates reliably, and has a long working life.

In accordance with the present invention, such objects may be achievedby a construction in which the rheostat is encapsulated by a resilientsheet of plastics material having an' inner conductive layer againstwhich an adjustable contact pin is arranged to press, whereby adjustmentof the contact pin establishes different values of electricalresistance.

In one form of such an arrangement, a winding of resistance wire isapplied to a flat insulating plate which is placed between two sheets ofplastics material welded together at the edges.

In another form of arrangement, a conductive layer is carried by onehalf of the sheet, and a resistive layer is carried by the other half,and the two layers overlie each other. I

By encapsulating the resistance wire or the resistance layer byenveloping it in the plastics sheet, an advantageous and effectiveprotection against external influences may be attained. Since suchsheets can easily be welded together, a simple and cost-savingproduction is ensured. Air, or other gas, or a liquid, enclosed betweenthe sheets ensures that when the position of the contact pin changes,the places previously pressed together by the contact pin are separatedwith certainty, so that the resistance values are faultlesslyreproducible, and exact measurement values are assured for the entireworking life. It is possible to employ thin, nonabrasive resistancelayers and conductive layers which, in order to simplify production, maybe applied by sputtering.

The encapsulated rheostat may be connected as a voltage divider if theconstruction is such that a conductive layer and a resistive layer arelocated side by side on the front half of the sheet, and a conductivelayer overlying both of the said two layers is located on the rear halfof the sheet, the contact pin being made so wide that it permitsbridging of the two mutually adjacent layers.

Appropriately, the ends of the layers or strips are provided with metalsupports for the attachment of leads or contact pins, for example bysoldering.

In the drawing:

FIG. 1 is a plan of one embodiment of a rheostat in accordance with theinvention, in the form of an encapsulated wire-type rheostat;

FIG. 2 is a longitudinal section through the rheostat shown in FIG. 1,along the line Il-Il;

FIG. 3 is a cross-section through the rheostat shown in FIG. 1, alongthe line IIIIII;

FIG. 4 is a plan of a second embodiment of a rheostat in accordance withthe invention, in the form of an encapsulated layer-type rheostat;

FIG. 5 shows folded half-sheets of the rheostat embodiment shown in FIG.4;

FIG. 6 is a cross-section along the line VI-VI of FIG. 4; and

FIG. 7 is a plan of a third embodiment of a rheostat in accordance withthe invention, in the form of a rheostat designed as a voltage divider.

In the embodiment shown in FIGS. 1 to 3, the rheostat consists of aplastics plate 1 serving as a support for a wire winding 2, two sheetsof plastic 3 and 4, and a contact pin 5 which presses the conductinglayer 6 at the inside of the sheet 4 against the winding 2 in order tomake localised contact, as will be seen from FIG. 2. The two sheets 3'and 4 are welded together at their edges at 7 so that the enclosedresistance 1, 2 cannot slip. The two leads 8 and 9 for the electriccurrent are hermetically embedded in the edge 7. The contact pin 5 isdisplaceable: reference numeral 10 designates its path. The air enclosedbetween the resilient sheets 3 and 4 ensures that, during movement ofcontact pin 5, the conductive layer 6 tends to be separated from thewinding 2 of the resistance, so that contact is made only at the placeat which the contact pin 5 is currently situated.

In the embodiment shown in FIGS. 4 to 6, two layers, of metal andresistance material respectively, are applied to two associated sheethalf-portions 15 and 16. A conductive metallic layer 17 is carried bythe upper half 15 and a resistive layer 18 is carried by the lower half16. Located at the ends of the layers 17 and 18 are metal electrodes 19and 20 to which lead-in conductors in the form of contact pins 21 and 22are secured by soldering. Following application of the layers, the sheethalf-portions 15 and 16 are folded and welded together at their commonedge 23, with the layers 17 and 18 inside, as will be seen in FIGS. 4and 6. The bottom edge 24 is formed by the fold which arises when thetwo halves 15 and 16 are closed together.

The mode of operation of this embodiment is the same as for theembodiment shown in FIGS. 1 to 3. Here again, the enclosed air (or otherenclosed gas, or liquid) ensures the separation of the two layers 17 and18 during the movement of the contact pin 5 (here omitted forsimplicity).

In the embodiment shown in FIG. 7, two layers are applied side by sideto the front plastics sheet, namely a conductive layer 30 and aresistive layer 31, these two layers being bridged by an oval contactpin 32. A conductive layer overlying both these layers 30 and 31 isapplied to the rear sheet. This embodiment is intended for use as avoltage divider, and has three connecting leads 33, 34 and 35.

The present invention is not limited to constructions corresponding tothose of the above-described embodiments illustrated in the drawing.Many possibilities of modification exist as regards the construction anddesign of the rheostat and the arrangement of its individual components,without departing from the scope of the present invention. As hasalready been mentioned, instead of air, a different gas, or a liquid,may be enclosed in the interior space between the two sheets such as 3and 4.

3 If required, several resistance strips may be provided on one sheet inplace of a resistance layer, whereby the rheostat construction may beadapted to a great number of operating conditions.

If, for example, in the FIG. 7 embodiment, the conductive layer appliedto the rear sheet is reduced to the width of the resistance layer 31over its entire length, and if the connection 34 is joined to this rearlayer, then in the lowermost position of the contact pin 32 a pilotlight, for example, can be additionally controlled, by way of theconnection 33. i

I claim:

I. A rheostat comprising a resistive element,

a resilient plastics sheet encapsulating the resistive element,

a conductive inner layer carried by the plastics sheet,

first contact means extending from the resistive element to the exteriorof the encapsulating plastics sheet,

second contact means extending from the conductive inner layer to theexterior of the encapsulating plastics sheet, and

a contact pin arranged to press on the encapsulating plastics sheet andadjustable to establish different values of electrical resistancebetween the first and second contact means.

2. A rheostat comprising a resistive element,

a resilient plastics sheet encapsulating the resistive element,

a conductive inner layer carried by the plastics sheet,

first contact means extending from the resistive element to the exteriorof the encapsulating plastics sheet,

second contact means extending from the conductive inner layer to theexterior of the encapsulating plastics sheet,

fluid interposed between the resistive element and the conductive innerlayer and tending to separate same, and

a contact pin that is arranged to press on the encapsulating plasticssheet to thereby establish localised contact between the conductiveinner layer and the resistive element, and is adjustable to establishdifferent value of electrical resistance between the first and secondcontact means.

3. A rheostat comprising a resistive element comprised of a flatinsulating plate I carrying a winding of resistance wire,

a resilient plastics sheet encapsulating the resistive element, saidplastics sheet being comprised of first and second sheet portions weldedtogether at their edges,

a conductive inner layer carried by the plastics sheet,

and

a contact pin that is arranged to press on the plastics sheet to'thereby establishv localised contact between the conductive inner layerand the resistive element, and is adjustable to establish differentvalues of electrical resistance.

4. A rheostat comprising an encapsulating resilient plastics sheetcomprised of first and second sheet portions folded against one anotherabout a common edge and welded together at their other edges,

a resistive element comprised of a resistive inner layer carried by thefirst sheet portion of the encapsulating plastics sheet,

a conductive inner layer carried by the second sheet portion of theplastics sheet and arranged to overlie the resistive element when thefirst and second sheet portions are folded against one another,

fluid interposed between the resistive element and the conductive innerlayer and tending to separate same, and

a contact pin that is arranged to press on the encapsulating plasticssheet to thereby establish localised contact between the conductiveinner layer and the resistive element, and is adjustable to establishdifferent values of electrical resistance.

5. A rheostat comprising an encapsulating resilient plastics sheetcomprised of first and second sheet portions hermetically securedtogether at their edges,

a resistive element comprised of a resistive inner layer carried by thefirst sheet portion of the encapsulating plastics sheet,

a first conductive inner layer carried by the first sheet portion of theencapsulating plastics sheet at a location alongside the resistive innerlayer thereof,

a second conductive inner layer carried by the second sheet portion ofthe encapsulating plastics sheet and overlying both the resistiveelement and the first conductive inner layer, and

a contact pin that is arranged to press on the encapsulating plasticssheet to thereby establish localised contact between the secondconductive inner layer and both the resistive element and the firstconductive inner layer, and is adjustable to establish different valuesof electrical resistance.

6. A rheostat according to claim 5, in which first contact means extendsfrom the first conductive inner layer of the encapsulating plasticssheet to the exterior of the encapsulating plastics sheet, and secondand third contact means extend respectively from opposite ends of theresistive element to the exterior of the encapsulating plastics sheet,for connection of the rheostat as a voltage divider.

7. A rheostat comprising an encapsulating resilient plasticssheetcomprised of first and second sheet portions sealed together at theiredges,

a resistive element comprised of a resistive inner layer carried by thefirst sheet portion of the encapsulating plastics sheet,

a first conductive inner layer carried by the first sheet portion of theencapsulating plastics sheet at a location alongside the resistive innerlayer thereof,

a second conductive inner layer carried by the second sheet portion ofthe encapsulating plastics sheet and overlying the resistive element,

first contact means extending from the first conductive inner layer ofthe encapsulating plastics sheet to the exterior of the encapsulatingplastics sheet, and second and third contact means extendingrespectively from opposite ends of the resistive e element to theexterior of the encapsulating plastics sheet, the second contact meansalso being connected to the second conductive inner layer,

a contact pin that is arranged to press on the encapsulating plasticssheet to thereby establish localised contact between the secondconductive inner layer and both the resistive element and the firstconductive inner layer, and is adjustable to establish different valuesof electrical resistance, and a pilot light connected to, and controlledby, the first contact means.

a 4: k a a

1. A rheostat comprising a resistive element, a resilient plastics sheetencapsulating the resistive element, a conductive inner layer carried bythe plastics sheet, first contact means extending from the resistiveelement to the exterior of the encapsulating plastics sheet, secondcontact means extending from the conductive inner layer to the exteriorof the encapsulating plastics sheet, and a contact pin arranged to presson the encapsulating plastics sheet and adjustable to establishdifferent values of electrical resistance between the first and secondcontact means.
 2. A rheostat comprising a resistive element, a resilientplastics sheet encapsulating the resistive element, a conductive innerlayer carried by the plastics sheet, first contact means extending fromthe resistive element to the exterior of the encapsulating plasticssheet, second contact means extending from the conductive inner layer tothe exterior of the encapsulating plastics sheet, fluid interposedbetween the resistive element and the conductive inner layer and tendingto separate same, and a contact pin that is arranged to press on theencapsulating plastics sheet to thereby establish localised contactbetween the conductive inner layer and the resistive element, and isadjustable to establish different value of electrical resistance betweenthe first and second contact means.
 3. A rheostat comprising a resistiveelement comprised of a flat insulating plate carrying a winding ofresistance wire, a resilient plastics sheet encapsulating the resistiveelement, said plastics sheet being comprised of first and second sheetportions welded together at their edges, a conductive inner layercarried by the plastics sheet, and a contact pin that is arranged topress on the plastics sheet to thereby establish localised contactbetween the conductive inner layer and the resistive element, and isadjustable to establish different values of electrical resistance.
 4. Arheostat comprising an encapsulating resilient plastics sheet comprisedof first and second sheet portions folded against one another about acommon edge and welded together at their other edges, a resistiveelement comprised of a resistive inner layer carried by the first sheetportion of the encapsulating plastics sheet, a conductive inner layercarried by the second sheet portion of the plastics sheet and arrangedto overlie the resistive element when the first and second sheetportions are folded against one another, fluid interposed between theresistive element and the conductive inner layer and tending to separatesame, and a contact pin that is arranged to press on the encapsulatingplastics sheet to thereby establish localised contact between theconductive inner layer and the resistive element, and is adjustable toestablish different values of electrical resistance.
 5. A rheostatcomprising an encapsulating resilient plastics sheet comprised of firstand second sheet portions hermetically secured together at their edges,a resistive element comprised of a resistive inner layer carried by thefirst sheet portion of the encapsulating plastics sheet, a firstconductive inner layer carried by the first sheet portion of theencapsulating plastics sheet at a location alongside the resistive innerlayer thereof, a second conductive inner layer carried by the secondsheet portion of the encapsulating plastics sheet anD overlying both theresistive element and the first conductive inner layer, and a contactpin that is arranged to press on the encapsulating plastics sheet tothereby establish localised contact between the second conductive innerlayer and both the resistive element and the first conductive innerlayer, and is adjustable to establish different values of electricalresistance.
 6. A rheostat according to claim 5, in which first contactmeans extends from the first conductive inner layer of the encapsulatingplastics sheet to the exterior of the encapsulating plastics sheet, andsecond and third contact means extend respectively from opposite ends ofthe resistive element to the exterior of the encapsulating plasticssheet, for connection of the rheostat as a voltage divider.
 7. Arheostat comprising an encapsulating resilient plastics sheet comprisedof first and second sheet portions sealed together at their edges, aresistive element comprised of a resistive inner layer carried by thefirst sheet portion of the encapsulating plastics sheet, a firstconductive inner layer carried by the first sheet portion of theencapsulating plastics sheet at a location alongside the resistive innerlayer thereof, a second conductive inner layer carried by the secondsheet portion of the encapsulating plastics sheet and overlying theresistive element, first contact means extending from the firstconductive inner layer of the encapsulating plastics sheet to theexterior of the encapsulating plastics sheet, and second and thirdcontact means extending respectively from opposite ends of the resistivee element to the exterior of the encapsulating plastics sheet, thesecond contact means also being connected to the second conductive innerlayer, a contact pin that is arranged to press on the encapsulatingplastics sheet to thereby establish localised contact between the secondconductive inner layer and both the resistive element and the firstconductive inner layer, and is adjustable to establish different valuesof electrical resistance, and a pilot light connected to, and controlledby, the first contact means.